In recent years, optical devices, such as light emitting diodes (LEDs), laser diodes, and UV photo-detectors have increasingly been used. Group-III nitride compounds, such as gallium nitride (GaN) and its related alloys have been known suitable for the formation of the optical devices. The large bandgap and high electron saturation velocity of the group-III nitride compounds also make them excellent candidates for applications in high-temperature and high-speed power electronics.
Due to the high equilibrium pressure of nitrogen at typical growth temperatures, it is extremely difficult to obtain GaN bulk crystals. Therefore, GaN layers and the respective LEDs are often formed on other substrates that match the characteristics of GaN. Sapphire (Al2O3) is a commonly used substrate material. FIG. 1 illustrates a cross-sectional view of a package component including LED 2. LED 2, which includes a plurality of GaN-based layers, is formed on sapphire substrate 4. Sapphire substrate 4 is further mounted on lead frame 6. LED 2 further includes electrodes 8 and 10 electrically connected to lead frame 6 through gold wires 12.
Because sapphire has a low thermal conductivity, heat generated by LED 2 cannot be dissipated through sapphire substrate 4 efficiently. The heat needs to be dissipated through the top end of LED 2, and through gold wires 12. However, since gold wires 12 are relatively long since they have to extend to lead frame 6, the thermal conductivity through gold wires 12 is also low. In addition, electrodes 8 and 10 occupy chip area, and hence the LED light output area is not optimized.